Seems I found the answer myself, haha
You can find these numbers in a message in your account. To find it:
- Log into your account
- Go to the heading called "View my submitted applications or profiles"
- Click on "Check status and messages"
- Scroll down to the table called “Correspondence”
- Click on the arrow in front of the message – it will open a drop-down menu with a link
- Click on the link to open the PDF message
- Make sure you are looking at the right message. If the text of the message doesn’t match the example above, check other messages in your account to find the right one.